With the advent of aircraft which are able to fly at relatively high speeds greater than Mach 1 plus the ability to climb to high altitudes, it is necessary to provide an oxygen system which will perform under these relatively harsh conditions. This is especially true in the case of military aircraft which must possess the ability to fly higher, faster, longer and with greater maneuverability than other aircraft. In supplying an oxygen system for the cockpit of military aircraft, it is necessary to have a system which will perform in an adequate manner and which will be relatively light in weight. Another criteria is that the system be relatively small in size inasmuch as the cockpit area, especially in pursuit or fighter aircraft, is relatively small. One method of supplying oxygen to the personnel on the aircraft is to store oxygen as a liquid. One advantage in using such a system is that liquid oxygen does not require a high pressure tank and the ratio of system volume and weight versus the usable material could be drastically reduced. However, the disadvantage to the use of such a system is that expensive equipment is required on the ground in order to handle the problems of handling the cryogenic liquid.
As an alternative to using the relatively expensive liquid oxygen system, it has been found possible to concentrate oxygen use of the air and provide it to the aircraft crew members via certain metal chelates. One such metal chelate which has been found to be effective in the generation of oxygen from air is cobalt bis(3-fluorosalicylaldehyde)ethylenediimine which is known as fluomine. This cobalt chelate compound can reversibly bind oxygen and generate it by absorbing the oxygen at low temperatures and desorbing it at higher temperatures. For example, fluomine will absorb oxygen at a maximum rate between 80.degree. and 100.degree. F. while the desorption of the oxygen will take place above about 180.degree. F. at relatively low pressures. A precursor to the aforementioned fluomine comprises 3-fluorosalicylaldehyde. This compound is prepared in a series of steps utilizing o-fluorophenol as the starting material.
Heretofore, the commercial source of o-fluorophenol was as a byproduct resulting from the production of p-fluorophenol. The production of the isomeric fluorophenols resulted from p-nitrochlorobenzene which was contaminated with o-nitrochlorobenzene and the yield of the isomeric fluorophenols from the isomeric nitrochlorobenzenes usually ranged from 45% to 80%. Other direct ways of obtaining the desired product starting with o-nitrochlorobenzene are multi-step and elaborate in nature utilizing such compounds as potassium fluoride and dimethylsulfoxide as well as nitric acid and sulfuric acid. By utilizing these compounds it is necessary to use relatively expensive and elaborate equipment and therefore, it is not economically feasible to obtain the desired product by utilizing these methods. As will hereinafter be set forth in greater detail, we have now discovered that it is possible to obtain a halogenated phenol such as o-fluorophenol by dealkylating a halogenated alkyl substituted phenol in a relatively simple manner.
This invention relates to a process for the dealkylation of a halogenated alkyl substituted phenol. More specifically, the invention is concerned with a process for dealkylating alkyl substituted fluorophenols. As hereinbefore set forth, halogenated phenols such as o-fluorophenol may be utilized as starting materials in preparing compounds which are useful for generating oxygen. In order to obtain a process whereby the desired chelate is prepared in an economical manner, it is necessary that all steps that are required for the production of the product be operated in like manner. Inasmuch as the starting material for preparing cobalt bis(3-fluorosalicylaldehyde)ethylenediimine is o-fluorophenol, it is necessary that this starting material costs as little as possible. The steps of synthesizing this starting material are relatively complex inasmuch as fluorobenzene must be subjected to a series of condensations and dealkylations in order to obtain the desired product.
It is therefore an object of this invention to provide an improved process for the dealkylation of halogenated alkyl substituted phenols.
A further object of this invention is to provide an improved process for the dealkylation of halogenated alkyl substituted phenols whereby the desired product comprising a halogenated phenol will be obtained in improved yields.
In one aspect an embodiment of this invention resides in a process for the dealkylation of a halogenated alkyl substituted phenol which comprises treating said phenol at dealkylation conditions in the presence of an acid acting catalyst, and recovering the resulted halogenated phenol.
A specific embodiment of this invention is found in a process for the dealkylation of a halogenated alkyl substituted phenol which comprises treating 5-t-butyl-2-fluorophenol at a temperature in the range of from about ambient to about 300.degree. C. and a pressure in the range of from about atmospheric to about 100 atmospheres in the presence of an acid acting catalyst comprising an aluminum chloride and an acceptor compound for the eliminated alkyl moiety comprising toluene, and recovering the resulting 2-fluorophenol.
Other objects and embodiments will be found in the following detailed description of the present invention.
As hereinbefore set forth the present invention is concerned with a process for the dealkylation of halogenated alkyl substituted phenols. The starting materials which comprise these compounds may be obtained from any source known in the art. For example, one method of approach for obtaining the starting materials may comprise alkylating a fluorobenzene with an olefin or an alkyl halide as the alkylating agent to introduce a bulky alkyl group, comprising a tertiary or secondary alkyl group, of which the tertiary alkyl group is preferred, in the para position. The alkylation of the fluorobenzene is preferably effected at temperatures ranging from about 0.degree. up to about 50.degree. C. or more in the presence of a conventional alkylation catalyst. Examples of alkylating agents which may be employed to form the desired product will preferably include olefins or alkyl halides containing from about 4 to 10 carbon atoms such as isobutylene, isopentene, isohexene, isoheptene, isooctene, isononene, t-butylchloride, t-butylbromide, 2-chloro-2-methylbutane, 2-bromo-2-methylbutane, 2-chloro-2-methylpentane, 2-bromo-2-methylpentane, 3-bromo-3-methylpentane, 2-chloro-2-methylhexane, 3-bromo-3-methylhexane, 3-chloro-3-methylheptane, 4-bromo-4-methylheptane, etc.
The thus formed para-alkylfluorobenzene may then be brominated at temperatures ranging from about 0.degree. to about 75.degree. C. in the presence of a catalyst such as iodine, iron, etc., to form a 4-alkyl-2-bromofluorobenzene. The latter compound may then undergo hydrolysis by treating the compound with water in the presence of catalysts such as potassium fluoride and cuprous oxide at elevated temperatures ranging from about 200.degree. to about 300.degree. C. under pressures ranging from about 1 to 100 atmospheres. The hydrolysis will result in the preparation of 5-alkyl-2-fluorophenols.
The aforementioned 5-alkyl-2-fluorophenols may then be subjected to dealkylation by treating the compounds with a dealkylation catalyst comprising an acid acting compound at dealkylation conditions which will include a temperature in the range of from about ambient (20.degree.-25.degree. C.) up to about 300.degree. C. or more and at pressures ranging from atmospheric to about 100 atmospheres. In the event that elevated temperatures within the upper limit of the range hereinbefore set forth are employed and super-atmospheric pressures are utilized, the latter may be afforded by the introduction of a substantially inert gas such as nitrogen, argon, helium, etc., into the reaction zone, the amount of pressure which is employed being that which is sufficient to maintain a major portion of the reactant in the liquid form. Examples of acid acting catalysts which may be employed to effect dealkylation will include such compounds such as Friedel-Crafts metal halides including aluminum chloride, ferric chloride, zinc chloride, stannic chloride, etc., protonic acids such as polyphosphoric acid, orthophosphoric acid, Solid Phosphoric Acid, p-toluenesulfonic acid, benzenesulfonic acid, acid clays such as acidic silicates, and acidic metal oxides such as alumina, silica-alumina, etc. In the preferred embodiment of the invention, in addition to the acid acting catalyst, the reaction zone will also contain an acceptor compound for the eliminated alkyl moiety, which may be transferred to the acceptor compound as a carbonium ion complex with the acid catalyst. The acceptor compound will preferably consist of an active aromatic compound containing substituents not readily eliminated or isomerized by the acid catalyst such as toluene, xylene, etc.
The process of the invention may be effected in any suitable manner and may comprise either a batch or continuous type of operation. For example, when a batch type operation is employed a quantity of the halogenated alkyl substituted phenol which may be prepared according to the description hereinbefore set forth and the acid acting catalyst, the latter being present in a molar excess in the range of from about 1.1:1 up to about 1.5:1 moles of catalyst per mole of phenol, are placed in an appropriate apparatus. The acid acting catalyst is present in slightly excessive amount in order that a portion of the catalyst remains uncomplexed with the phenolic group in order to effect the dealkylation of the phenol. In addition, if so desired, an acceptor compound such as toluene as hereinbefore described, is also present in the reaction vessel. Following the addition of the reactant catalyst and acceptor compound, the apparatus and contents thereof are then heated to the desired temperature within the range hereinbefore set forth and continuously agitated during the dealkylation time which may range from about 0.5 up to about 30 hours or more in duration. At the end of this period of time the apparatus and contents thereof are allowed to return to room temperature and the reaction mixture subjected to conventional means of separation whereby the desired halogenated phenol is separated from any unreacted starting materials, olefin, catalyst and the alkylated acceptor compound by-product.
It is also contemplated within the scope of this invention that the process for the dealkylation of the halogenated alkyl substituted phenol may be accomplished in a continuous manner of operation. When such a type of operation is used the halogenated alkyl substituted phenol is continuously charged to a reaction vessel which is maintained at the proper operating conditions of temperature and pressure. In addition the reaction vessel will also contain an acid acting catalyst of the type hereinbefore set forth in greater detail. If so desired the acceptor compound such as toluene may also be charged to the reactor through a separate line or, if so desired, it may be admixed with the halogenated alkyl substituted phenol prior to entry into said reactor and the resulting admixture charged thereto in a single stream. In the event that the acid acting catalyst is in solid form the dealkylation may be effected using a fixed bed method in which the catalyst is disposed in the reactor as a fixed bed and the halogenated alkyl substituted phenol is passed through said bed in either an upward or downward flow. Other conventional types of continuous operating procedures may also be employed. When employing such continuous processes for effecting the dealkylation, the reactor effluent is continuously withdrawn from the reaction zone after passage of the desired reaction time and subjected to conventional means of separation whereby the desired halophenol is separated and recovered while any unreacted starting material, catalyst, and alkylated acceptor by-product compound are also recovered and the unreacted starting material, in particular, recycled to the reaction zone to form a portion of the feedstock.
Some examples of halogenated tertiary or secondary alkyl substituted phenols which may undergo dealkylation to form the corresponding ortho-halophenol will include 5-t-butyl-2-bromophenol, 5-t-butyl-2-fluorophenol, 5-t-butyl-2-iodophenol, 5-sec-pentyl-2-bromophenol, 5-sec-pentyl-2-fluorophenol, 5-sec-pentyl-2-iodophenol, 5-sec-hexyl-2-bromophenol, 5-sec-hexyl-2-fluorophenol, 5-sec-hexyl-2-iodophenol, 5-sec-heptyl-2-bromophenol, 5-sec-heptyl-2-fluorophenol, 5-sec-heptyl-2-iodophenol, etc. It is to be understood that the aforementioned halogenated alkyl substituted phenols and corresponding halophenols are only representative of the class of compounds which may be used in the present process, and that the process of the present invention is not necessarily limited thereto.